The invention concerns a rotary joint to be used for controlling the vane angles of a water turbine or a propeller pump.
A water turbine has a rotating hub provided with a number of vanes and arranged in a tube or the like with flowing water. The rotary energy obtained is transmitted to a generator for electric current. The rotary energy obtained is, of course, totally dependent on the amount of flowing water and the potential energy head that can be utilized. The amount of water may vary considerably which means that the turbine will operate with different flows at different times. As the turbine is designed to have its maximum efficiency at a certain volume of flow and a certain head, the energy of the water will be more or less well utilized.
By designing the vanes adjustable, which means that the vane angle with relation to the water flow may be varied, there is a possibility to optimize the efficiency within a relatively wide range of water flow. In older turbine equipment, where the turbine through an elongated shaft is connected to a "dry" generator, the adjustment of the vanes has been relatively easy to obtain by help of hydraulic or other mechanical transmission means along the shaft. However, recently an entirely new type of turbine/generator has been utilized. The turbine and the generator are integrated into one unit so that it may be easily hoisted up from the water tube for service. This type of energy generator is especially suitable for small volumes and relatively low heads.
Such a turbine when provided with adjustable vanes, must be easily serviceable. Also, the monitoring impulses that cause adjustments of the vane angles, must be transmitted from a non-rotating to a rotating element in its operating environment.